It is the purpose of this study to establish the proper dietary and metabolic conditions necessary to induce experimental atherosclerosis in various species which has characteristics similar to that of man. In three species, the dog, miniature swine, and Patas monkey, this has been accomplished. The source of dietary fat has been found to have a profound effect in the type, distribution, and severity of the atherosclerosis. The atherosclerosis produced by diets containing beef tallow, in addition to being severe, is associated with gross arterial thrombosis and occlusive vascular disease.